A person will be out of Islam if he denies intentionally and on purpose any one of the Islam known 5 pillars.
see related questions for more information on Islam 5 pillars.
-ELO-
Life in Islam is about pleasing Allah. Anyone can please themself, but are you strong enough to stop doing things the way you like, and do them the way your creator tells you? A Muslim should be...
Well, Judgement Day happens, determining whether you go to heaven or hell. There is some sort of huge chasm (I think) and there is a bridge that's more like the thinnest tightrope you've ever seen....